1. Field of the Invention
The invention relates to a method and system for fabricating a liquid crystal film in a brightening film of a liquid crystal display, and a method for fabricating the brightening film using the liquid crystal film.
2. Description of the Related Art
With a growing popularity for television, personal computer (PC) and handheld product, Liquid crystal display (LCD) has been developed and widely applied in flat televisions, notebook computers, monitors, cell phones, personal digital assistants, and information home appliances. In the development of LCD, products with high brightness and low power consumption still remain the most important trends in the future. However, a color filter, a polaroid glass, and films having high absorption for light are adopted in a thin film transistor liquid crystal display (TFT LCD) to satisfy the full color requirement. The Polaroid glass reduces the light intensity by about 50%, and the color filter further reduces the light intensity by about 66%. Therefore, the manufacturer of the related field has been working on how to achieve higher light penetration power by effectively using the same backlight source.
Currently, it is achieved by adopting multiple-film optical interference theory, where two transparent polymeric materials with different refractive index are laminated and extended in one single direction such that the refractive index of the laminated materials are similar to each other, while in the direction orthogonal to the extension direction, the inherent refractive index of these two materials are maintained. When the laminate is in use, a polar ray O vertical to an optical axle resonance direction of the laminate is allowed to pass through the laminate, while a polar ray E parallel to the optical axle resonance direction is reflected. The reflected E ray is further reflected by a reflecting sheet in a backlight module, and the E ray is transformed into the O ray, so that the transformed O ray can pass through the film to achieve recycling of the light source.
Furthermore, a cholesteric liquid crystal reflective brightening film provides an alternative to increase brightness of LCD based on a theory that the cholesteric liquid crystal has a helix structure that results light reflection at a specific wavelength λ0. And the reflective wavelength λ0, the pitch P, and the liquid crystal average refractive index na can be related by Maxwell theory as below:λ0=na×P So, the reflective wavelengths is:Δλ=Δna/na×P 
Theoretically, for a 100% non-polar incident light incident to a cholesteric liquid crystal having right-handed helix structure, 50% of right-handed circular polar light reflects and 50% of left-handed circular polar light passes through the crystal. When the light enters a reflective cholesteric liquid crystal brightening film from a backlight module, only the circular polar light that spirals opposite to the helix structure of the liquid crystal can pass through the liquid crystal, while the circular polar light that spirals along the helix structure of the liquid crystal is reflected back to the backlight module. The reflected circular polar light is reflected again by a reflecting sheet of the backlight module and the reflected circular polar light is then transformed to the circular polar light with opposite helix so as to pass through the liquid crystal, achieving recycling of the light source.
However, the circular polar light that passes through the cholesteric liquid crystal cannot be directly used for LCD. A quarter phase delay film is needed to transform the circular polar light into a linear polar light that is used for LCD.
In massive production of the cholesteric liquid crystal brightening film, cholesteric liquid crystal molecules with different pitches are applied in layers over a plastic substrate. The different pitches of layered material allow passage of lights of various wavelengths over the visible light region. When the light source of the backlight module and cholesteric liquid crystal brightening film achieves increase in brightness and illumination efficiency.
In order to achieve theoretical right-handed polar light reflection of 50% and left-handed polar light reflection of 50% after the film is formed, the cholesteric liquid crystal molecules must align with each other on the plastic substrate to form a helix structure, like springs inside the spring bed.
Typically, an orientation film is applied on the substrate, and the orientation layer is mechanically rubbed clockwise with a nap roller in a contact manner, so that the liquid crystal molecules are well orientated in a direction. According to this method, the orientation film is applied beforehand and is cured under high temperature. If the orientation layer were formed on a glass substrate, no deformation occurs during high-temperature curing. However, if the orientation layer were formed on a plastic substrate, then the plastic substrate would deform and melt under high temperature curing.
The glass substrate is mainly adopted in formation of a display panel. Two glass substrates with orientation films are provided. When the liquid crystal material is filled between the substrates, upper and lower orientation boundaries are provided. By means of appropriate annealing, liquid crystal molecules are easily orientated with limitations from the upper and lower orientation boundaries. However, when the plastic substrate in the rolls is coated, only one face is coated without forming the upper and lower orientation boundaries to achieve well orientation. On the other hand, the orientation film cannot be cured on the plastic substrate. Therefore, it is not impossible to perform a mechanical rubbing by the nap to orientate the liquid crystal. Since the orientated liquid crystal structure is essential to the optical properties of cholesteric liquid crystal, orientation methods by electric field, magnetic field, or stress application other than coating of the orientation film may be adapted to achieve orientation of the liquid crystal molecules. However, for the fabrication that involves continuous coating in rolls, these orientation methods certainly pose limitation for the massive production.
Therefore, it is an urgent need for the manufacturer to develop a method and a system for fabricating the orientated liquid crystal molecules in massive manner.